Use Cases
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Roles of Use Cases
A use case is a set of activities that
produce some output result
Describes how the system reacts to an
event that triggers the system
Trigger -- event that causes the use case
to be executed
Event-driven modeling – everything in
the system is a response to some
triggering event
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Modeling Use Cases
Complete piece of functionality
Main flow/Main success scenario
Subflows
Extensions/Alternate flows
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Role of Use Cases
All possible responses to the event are
documented
Use cases are helpful when the situation
is complicated
4
Sample Format for a
Written Use Case
Title – descriptive name, matches name
in use case diagram
Primary actor – usually a user role
Stakeholders – any group or individual
with an interest in the function of the use
case
Precondition – conditions that must be
satisfied in order to execute the use case
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Sample Format for a
Written Use Case - 2
Minimal guarantee/Postcondition – outputs
that can be expected if the service attempt
failed
Success guarantee/Postcondition –
outputs that can be expected if the service
succeeds
Trigger – an event or action that initiates the
use case
Main success scenario – description of
sequence of interactions between actor and
use case during the use case execution
Extensions – detailed description of how
errors are dealt with
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A sample
written use
case
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Building Use Cases
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Step 1:
Identify the major use cases
Activities
Start a use case form for
each use case
If more than nine, group
into packages
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Typical Questions Asked
Ask who, what, and where about the tasks and their
inputs and outputs:
What are the major tasks performed?
What triggers this task? What tells you to perform this
task?
What information/forms/reports do you need to perform
this task?
Who gives you these information/forms/reports?
What information/forms/reports does this produce and
where do they go?
Sample List of Events-Actions Based
on Requirements Definition
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Step 2: Identify the major steps within
each use case
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Activities
Typical Questions Asked
For each use case, fill
in the major steps
needed to process the
inputs and produce the
outputs
Ask how about each use case:
How do you produce this report?
How do you change the information on the report?
How do you process forms?
What tools do you use to do this step (e.g., on
paper, by email, by phone)?
Step 3:
Identify elements within steps
Activities
For each step, identify
its triggers and its
inputs and outputs
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Typical Questions Asked
Ask how about each step
How does the person know when to perform this
step?
What forms/reports/data does this step produce?
What forms/reports/data does this step need?
What happens when this form/report/data is not
available?
Step 4:
Confirm the use case
Activities
Typical Questions Asked
For each use case,
Ask the user to execute the process using the
validate that it is correct written steps in the use case – that is, have the
and complete
user role-play the use case
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Summary
Use cases contain all the
information needed for process
modeling, but are easier for users to
comprehend
Use cases are created in an iterative
cycle of steps until they are
considered accurate and complete
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Exercise: Use Cases
Document four use cases from your
project (the most important ones):
• two from an end-user perspective
• two from an administrator perspective
Think about the main and alternative
flows. Think about the “happy case”.
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